Unless your really really strapped for cash, I would rent a car. Makes the whole trip much easier and much easier to do the other tournaments and see the city. It's not like New York.. free parking just about everywhere, the city is very easy to get around and hard to get lost. Even if your staying downtown, you'll still some kind of transportation to get the cashman center, the silver nugget, the orleans, and samstown. Seach for a good car deal and pull the trigger. Your trip will be much more enjoyable and probably not that much expensive than if you paid for buses and taxi's.
